The green tag on the container indicates that the product inside is no longer fresh.
Chao Zhang

What if you never had to do a smell test for spoiled milk again? Instead of having to take a whiff of the sour liquid, you could just check the color of a small tag placed on the container.

This is exactly what researchers at Peking University in Beijing, China, are working on: color-coded "smart tags."

These corn kernel-sized tags can be stuck to containers of food or medicine and have the capabilities of determining whether the food has gone bad or if the medications are still active. What's more, these tags will reportedly cost less than one penny each.

"This tag, which has a gel-like consistency, is really inexpensive and safe, and can be widely programmed to mimic almost all ambient-temperature deterioration processes in foods," lead researcher Chao Zhang said in a statement.

While most food and medicine have expiration labels, sometimes products are subjected to unanticipated high temperatures that could lead to early spoiling. Zhang said the smart tags could even take these sorts of variables into account. The color-coding on the tags would indicate the quality of the food or medicine on a range of 100 percent fresh to 100 percent spoiled.

"In our configuration, red, or reddish orange, would mean fresh," Zhang said. "Over time, the tag changes its color to orange, yellow and later green, which indicates the food is spoiled."

The science behind the tags is based on tiny non-toxic metallic nanorods that change color as they react to the length of time microbes grow in food. For example, "the gold nanorods we used are inherently red, which dictates the initial tag color," Zhang said.

The smart tag research was presented on Monday at a national meeting of the American Chemical Society. The smart tags aren't yet available, but the Peking University researchers said they are currently in the process of reaching out to manufacturers.

About the author

Dara Kerr is a staff writer for CNET focused on the sharing economy and tech culture. She grew up in Colorado where she developed an affinity for collecting fool's gold and spirit animals.
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